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May 24, 2011 -- Otherwise healthy middle-aged women newly diagnosed with a heart rhythm problem known as atrial fibrillation are at increased risk of premature death, a study shows.

The study is published in the Journal of the American Medical Association.

Many studies have found older people with atrial fibrillation have a higher risk of dying. However, the risk linked with new-onset atrial fibrillation in middle-aged people has not been well studied, says researcher David Conen, MD, MPH, assistant professor of internal medicine at University Hospital, Basel, Switzerland.

''This large group [of middle-aged people] was generally believed to have a benign outcome," he says. "We now show that [younger] participants with new-onset atrial fibrillation had an approximately twofold increased risk of death compared to women without new-onset atrial fibrillation."

But it is crucial to put the finding in perspective, he tells WebMD. After other cardiovascular risk factors were accounted for, about 2.1% of all deaths could be blamed on the abnormal heart rhythm.

Nevertheless, the finding provides an important practical message, says Teresa S.M. Tsang, MD, a professor of medicine at the University of British Columbia. She co-authored an editorial to accompany the study. "Atrial fibrillation is not benign," she says.

It should be treated when detected, she says. And coexisting problems such as high blood pressure should also be controlled, she says.

What Is Atrial Fibrillation

About 2.2 million Americans have the abnormal heart rhythm, according to the American Heart Association.

In the condition, the two small upper chambers of the heart, called the atria, quiver instead of beating regularly. As a result, blood is not pumped efficiently through the heart. It may pool and subsequently clot. If a clot leaves the heart and travels to the brain, a stroke can occur.

Atrial fibrillation is sometimes diagnosed after a patient complains of symptoms such as palpitations. It may also be detected during a physical exam or during an electrocardiogram.

The risk of getting the abnormal rhythm increases with age. Up to 5% of people age 65 and older have atrial fibrillation, the American Heart Association estimates.

When it is diagnosed, the condition is treated in a variety of ways. Medication can slow the rapid heart rate or even restore normal rhythm. Blood thinners may be required to reduce the risk of stroke.

Tracking Risks of Atrial Fibrillation

Conen and colleagues evaluated nearly 35,000 women enrolled in the Women's Health Study from 1993 to 2010. All were over age 45 when they enrolled in the study. The median age was 53 (half were younger, half older).

During a median follow-up of 15.4 years, 1,011 women developed the abnormal rhythm. There were 1,602 deaths from all causes, including 63 deaths in women with newly diagnosed atrial fibrillation.

After taking age into account, the risk of death from all causes, including cardiovascular causes, was significantly higher among the women who developed atrial fibrillation than those who did not.

One take-home point of the study, Conen tells WebMD, is for women newly diagnosed with atrial fibrillation to pay attention to co-existing risk factors such as high blood pressure and high cholesterol.

Trying to prevent the abnormal heart rhythm from developing in the first place is important too, says Conan, who reports receiving research grants from Boehringer Ingelheim, Novartis, and Sanofi-Aventis

Besides controlling weight and blood pressure, it is important not to smoke, to keep cholesterol at healthy levels, and to control diabetes if it occurs, says Tsang, who is also director of cardiovascular research at Vancouver General Hospital.

Until this study "we actually knew very little about this condition in middle-aged women," she says. "Newly identified [atrial fibrillation] in seemingly healthy women should be taken seriously and treated aggressively."